Camshaft phasers for varying the timing of combustion valves in internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from the internal combustion engine's crankshaft. A second element, known generally as a camshaft plate, is mounted to the end of an internal combustion engine's camshaft. A common type of camshaft phaser used by motor vehicle manufactures is known as a vane-type camshaft phaser. U.S. Pat. No. 7,421,989 shows a typical vane-type camshaft phaser which generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve, in accordance with an engine control module, to either the advance or retard chambers, to change the angular position of the rotor relative to the stator, and consequently the angular position of the camshaft relative to the crankshaft, as required to meet current or anticipated engine operating conditions.
While vane-type camshaft phasers are effective and relatively inexpensive, they do suffer from drawbacks. First, at low engine speeds, oil pressure tends to be low, and sometimes unacceptable. Therefore, the response of a vane-type camshaft phaser may be slow at low engine speeds. Second, at low environmental temperatures, and especially at engine start-up, engine oil displays a relatively high viscosity and is more difficult to pump, therefore making it more difficult to quickly supply engine oil to the vane-type camshaft phaser. Third, using engine oil to drive the vane-type camshaft phaser is parasitic on the engine oil system and can lead to requirement of a larger oil pump. Fourth, for fast actuation, a larger engine oil pump may be necessary, resulting in additional fuel consumption by the internal combustion engine. Lastly, the total amount of phase authority provided by vane-type camshaft phasers is limited by the amount of space between adjacent vanes and lobes. A greater amount of phase authority may be desired than is capable of being provided between adjacent vanes and lobes. For at least these reasons, the automotive industry is developing electrically driven camshaft phasers.
One type of electrically driven camshaft phaser being developed uses a harmonic drive gear unit, actuated by an electric motor, to change the angular position of the camshaft relative to the crankshaft. Examples of such camshaft phasers are shown in U.S. Pat. Nos. 5,417,186; 6,328,006; and 7,421,990. However, none of these examples provide oil from the internal combustion engine in order to lubricate the harmonic gear unit and other components of the camshaft phaser that may benefit from oil to increase durability of the camshaft phaser.
What is needed is an eVCP which utilizes oil from an internal combustion engine to lubricate the harmonic gear drive unit and other elements of the eVCP. What is also needed is such a camshaft phaser that receives only enough oil from the internal combustion engine to provide long term durability of the eVCP while not requiring increased capacity of a lubrication system of the internal combustion engine.